The invention relates to a method and apparatus for measuring the angular velocity (or rpm) of a measuring body, the distance of which body from a sensor varies periodically as the body is rotated, by emitting a distance signal dependent on said distance by the sensor and by converting the distance signal to a frequency-dependent signal in a converter circuit.
Apparatuses of this type for measuring angular velocity are employed in motor vehicles on a large scale, in particular for measuring the rpm of a timing shaft, a crankshaft, a primary shaft of the transmission, or a wheel axle. In such an apparatus for measuring angular velocity, typically, a measuring body in the form of a spur gear generates a periodic distance signal in the sensor device, the frequency of which signal is proportional to the rpm of the measuring body, and which signal is converted in the converter circuit to a frequency-dependent rpm signal. With such known apparatuses for measuring angular velocity, however, it is very difficult to measure very low rpms, because the low frequencies thereby produced cannot be measured rapidly and accurately. If one seeks to alleviate this problem by increasing the number of teeth on the measuring body, one must increase the size of the measuring body (although the sensor may remain the same size); moreover, at high rpm the upper frequency of the converter circuit will soon be reached.
The underlying problem of the present invention is to devise a method and apparatus for measuring the angular velocity (or rpm) of a measuring body, the distance of which body from a sensor varies periodically as the body is rotated, such that it is possible to measure rpm over a wide range including rpm values close to zero.